Alumina production



United States Patent 3,429,660 ALUMINA PRODUCTION Carl D. Keith, Summit,N.J., and Kurt W. Cornely, Islyosset, N.Y., assignors to EngelhardIndustries,

c. No Drawing. Filed Dec. 8, 1964, Ser. No. 416,891 US. Cl. 23-143 8Claims Int. Cl. C01f 7/42 ABSTRACT OF THE DISCLOSURE An aqueous hydrousalumina slurry containing boehmite and amorphous hydrous alumina is madeby hydrolyzing aluminum having a surface area of about 75,000 to1,000,000 square millimeters per gram, in the presence of awater-soluble carboxylic acid, for instance, formic acid, at atemperature of about 60 to 250 C. The mole ratio of the reactants can beabout 1 mole of acid per 2 to 30 gram-atoms of aluminum and at leastabout 18 moles of water. Incremental addition of the aluminum and acidis especially advantageous.

This invention relates to the preparation of alumina and morespecifically to a method for the preparation of alumine. by theinteraction of Water and aluminum metal in the presence of an acid. Inthis invention aluminum, in a state of extremely fine subdivision andhigh surface area, is contacted with water, preferably at a temperaturenear the boiling point of Water, in the presence of a non-oxidizingacid. The reaction produces a fine particle hydrous alumina slurry inwater, the hydrous alumina being either one or both of the valubleboehmite and amorphous forms, suitable for use as precursors for highlypreferred catalysts and catalyst bases.

The art suggested reacting aluminum metal with Water under a Widevariety of conditions to form alumina. In one group of these processes,very high temperature and pressure conditions, as Well as conditions ofextreme agitation are employed to produce the alumina and often thereaction does not go to completion, that is, a significant amount offree aluminum is left at the end of the reaction. In another group ofprocesses, more moderate temperatures and pressures are employed butthese processes usually require the presence of mercury or other heavymetal promoters to achieve commercially useful results. See, forexample, US. Patent 3,003,952. In either of these types of processes, ithas been proposed that aluminum powder may be employed. It has now beenfound that aluminum in a very fine state of subdivision and with a veryhigh surface area may be reacted with liquid phase Water to formalumina, and mercury or other promoting metals should be avoided as theyactually retard the reaction. It has also been found that the reactionshould preferably take place at temperatures near the boiling point ofwater and even more advantageously at about atmospheric pressure.

This invention is advantageous in its speed and in the fact that thecompleteness of the reaction (usually essentially 100%) and its freedomfrom reliance on nonvaporizable reagents gives a purer product for usessuch as in catalysts Where purity is often essential. This invention canprovide the alumina as a much more concentrated Water slut'ry than otherprocesses; often the slurry contains about 33-15% alumina, say about542%, but by the proper choice of reaction procedures, can give a slurrycontaining as high as about 11 to 12% or more alumina. Under a preferredset of conditions the alumina obtained from the slurry will consistessentially of hydrous alumina in the amorphous and boehmite forms andin the proportions of about one part amorphous to 24 parts boehmite, v

3,429,660 Patented Feb. 25, 1969 which is advantageous in many catalystsituations. The boehmite is generally of the small crystallite type, sayof about 15-35 A.

In this invention the aluminum employed is finer than most materialsreferred to as powder and the metal used has a surface area of aboutthousand to 1 million square millimeters per gram, preferably about150,000 to 600,000 mm. /gm. The aluminum may often be in the generalparticle size range of about 2 to 100 microns. Preferably at least about50% of the particles are of about 10 to 40 microns. The aluminum isusually one where at least about can pass a 325 mesh sieve (US. StandardSieve Series).

An aluminum suitable for the process of this invention is commerciallyavailable for use, for example, in adhesives. Usually it has a puritygreater than about 99% or even greater than 99.9% and may be obtained byatomiz inz molten aluminum in air. It often will have a particle sizerange primarily in the 5 to 50 micron range, for instance as follows:

Particle size (microns): Proportion of particles (percent) If thealuminum contains more than about 15 of particles in the range of 44-70or an appreciable amount of particles above 70 the reaction may requirea longer time to go to completion or may never go to completion, underthe preferred conditions of acid concentration. Too fine a particle sizemay lead to temperature control problems in the conversion procedure.

In the process of this invention, an acid is supplied to the reactionbetween aluminum and water but the amount of acid is insufiicient tosupply one acid ion for each two atoms of aluminum, that is to say, theratio of aluminum atoms to acid anions is greater than 2/1 and may be upto about 30/1 or more. Preferably, the ratio of aluminum atoms to acidanions is about 5-15 or even about 25/1. Usually the reaction will beconducted at a pH below about 4.1.

In order to avoid the presence of ions which would require extensinveWashing of the product to yield an acceptable catalyst material, theacid employed may be one which will vaporize or be oxidized during thedrying or other processing step of the alumina manufacture or decomposeto materials vaporizable under these conditions. Nitric or otheroxidizing acids give a number of poor results as shown below, in partdue to interaction with the hydrogen produced in the reaction, asexplained below. Therefore, water-soluble, organic carboxylic acidsgenerally are preferred for the reaction, in particular, the solublesaturated lower fatty acids, say of l-2 carbon atoms, e.g., formic acid,acetic acid, trichloroacetic acid, etc. The monobasic acids areadvantageous and formic acid is the most preferred.

The concentration of acid in the reaction mixture at any point of thereaction may have an effect on the product distribution. The preferredmonohydrate hydrous amorphous alumina mixture is produced When theformic acid is very dilute, that is sufiicient to keep the pH of thereaction Within the range of about 3 to 4. Above this pH, the productmay tend to gel before the reaction is complete, thus delaying orpreventing completion. Also, the formic acid may tend to decomposeexcessively. It is often preferably, therefore, to use formic acid of amolarity of about 0.6-0.7 and also to add the formic acid incrementallyduring the course of the reaction so that the pH will stay within thedwired range.

Water in the liquid phase is present in the reaction mixture in amountssuificient to keep the mixture fluid. Generally, the ratio of water toaluminum will be at least about 9 moles of water per gram atoms ofaluminum, preferably about 2030/ 1. Higher amounts of water, that is,greater than about 30 moles per gram-atom of aluminum, say up to about60 or 75 moles, do not seem to offer any advantages to offset the needfor a larger reactor volume and a need to filter the resulting aluminaproduct to get a practical slurry concentration. Where aluminum is addedincrementally to the reaction mixture, it is possible and sometimesfeasible to use slightly less than 10 moles of water per gram atom ofaluminum.

The total reaction mixture thus usually contains a ratio of about onemole acid to about 2-30 gram-atoms of aluminum metal to at least about18, e.g. about 18 to 2,250 moles, of water. Preferably about 100-750moles of water and 5-15 gram atoms of aluminum are often used per moleof acid.

As mentioned, it may often be preferred to add the aluminum metal and/or the formic acid incrementally to the water during the course of thereaction. Such incremental additions of formic acid and aluminum metalshould preferably be at such rates that the approximate 1/5-15/100-750acid-aluminum-water ratio described above and the 3 to 4 pH aremaintained essentially throughout the reaction. Such manipulationsaccelerate the rate of reaction and provide for improved concentrationof A1 in the product slurry. For ease of handling, the fine aluminumpowder may often be transported to the reaction zone as a slurry inwater.

Reaction conditions generally include a temperature of at least about 60C., although the reaction may be slow below the preferred range of about90-110 C. The reaction can readily take place at a higher temperature,e.g. up to about 500 pounds steam pressure, that is, about 250 C., butpressurized equipment is required at this temperature to keep thenecessary liquid phase. At the preferred temperature or below, oneatmosphere pressure is satisfactory and water may be refluxed during thereaction. Often the reaction produces a relatively highly concentratedalumina slurry which can be sent immediately to further processing, e.g.drying, addition of catalytic promoting metals, etc. Sometimes, however,it may be desirable to further concentrate the slurry and in such casesadditional acid may be used after the reaction to peptize the aluminaparticles. Subsequent evaporation can then be employed to obtain apourable thick slurry containing up to about 60% or more hydrousalumina.

The following examples are cited to illustrate further the fine aluminumpowder may often be transported to benefits afforded through theutilization thereof.

Example I To a 1-liter, fluted, three-necked Pyrex flask fitted with ahigh-speed two-bladed agitator, a reflux condenser and a thermoregulatorwas added 500 cc. of deionized water, 1 cc. of 88% formic acid and 6.25grams of atomized aluminum metal (99.5% purity, surface area of 310,000mm. /g.; particle size distribution of 5-50/L). The agitator was set torotate at 1800 r.p.m. and the reaction was initiated at roomtemperature. As the temperature rose, the rate of hydrogen productionincreased. The temperature was allowed to reach 100 C. and maintained atthis temperature. At the end of 1.5 hours an additional 6.25 grams ofaluminum metal and cc. of 0.684 Molar formic acid were added to thereaction mixture. Further equal additions of aluminum metal were made at3.5, 4.5, 5 and 6 hours total reaction time, so that a total of grams ofaluminum metal had been added. During the time interval of 2-6 hours,0.684 Molar formic acid solution was added until a total of 0.095 molesof 100% formic acid had been added. The reaction was allowed to continuefor a total of 12 hours at the end of which the reaction mixture wascompletely free of aluminum.

The pH of the reaction mixture was shown to be 3.4. The pH was adjustedto 8.4 With a 1:10 dilution of ammonium hydroxide in water. The mixturegelatinized as the pH was increased. The gelled product was filtered anddried at 110 C.

X-ray diffraction analysis showed the dried product to consist of 22%amorphous hydrous alumina and 78% boehmite with a crystallite size of27.8 Angstroms. The dried product had a surface area of 255 m. g. (BET).

Example II In this example the method of operation was identical to thatcited in Example I, with the exception that less formic acid was added.The total moles formic acid added was 0.071 mole. In this case the totalreaction time required for the reaction to go to completion was 18hours. Thus a lower acid concentration increases the itme required forthe reaction to go to completion using the same aluminum metal andtemperature.

Analysis of the product showed a composition of 24% amorphous alumina.and 76% boehmite with a crystallite size of 28.5 Angstroms.

Example III In order to further study the effect of the acidconcentration on the time required to complete the reaction, a run wascarried out similar to that cited in Examples I and II but with theexception that the total formic acid to be added was 0.067 mole. At theend of 24 hours, the reaction mixture still contained traces ofunreacted aluminum. The indicated degree of completeness as calculatedfrom the hydrogen production was 98.5%. The reaction product wasisolated by decantation from the unreacted aluminum, dried and analyzed.The product composition was found to be 23% amorphous alumina, 77%boehmite, with a crystallite size of 33.5 Angstroms and a surface areaof 248 mF/g. (BET).

Example IV The procedure in this example was identical with that citedin Example I with the exception that instead of formic acid, 0.1 Normalnitric acid was used.

Initially the reactor was charged with 10 grams of aluminum metal (550,uparticle size distribution, BET surface area of 210,000 mm. /g.); 1.56cc. (0.058 mole) of concentrated nitric acid and 400 cc. of de-ionizedwater. The reaction was run at 100 C. and atmospheric pressure. Atconversion a marked increase in viscosity occurred and additionalquantities of 0.1 N nitric acid were added to give a total of 30 cc.

At the end of two hours total reaction time, there was a 34% conversionand an additional quantity of aluminum metal was added (5 grams, 0.185mole). The ratio of materials, therefore, was 0.088 mole nitric acid/0.555 gram atoms aluminum to 27.8 moles water. At the end of 6 hours thereaction was terminated, when extremely slow hydrogen production becameapparent, showing that the reaction was approaching inhibition and thatit would probably never go to completion. The reaction product wasisolated from the unreacted aluminum metal. The total conversion at thistime was 58.6%. The isolated product was dryed and analysed. Analysisshowed the composition: amorphous alumina 13%; boehmite 84%, crystallitesize 88.9 A. and a total of 3% trihydrates. pH of the reaction mixtureat termination was 7.6.

Example V To show the effect of high formic acid concentrations, areactor flask, as described in Example I, was provided with grams (1.85moles) of atomized aluminum metal (5 50 particle size distribution,99.5% purity, surface area of 230,000 mm. /g., 250 ml. of 88% formicacid and 250 ml. of de-ionized water, a gram mole or atom ratio of acidto aluminum to water of 1/ 0.322/ 2.77. The reaction flask was heatedexternally to C. and held at this temperature. The reaction mixture wasagitated by means of a twobladed propeller type agitator. The reactionwas allowed 6 to go to 60% completion at which time it was terminatedtion mixture was added a solution of mercuric chloride, when it becameapparent that the reaction rate was rapidly equivalent to 0.1 gram(0.037 mole) HgCl to 0.37 mole decreasing. The reaction product wasisolated from the of aluminum metal. large amount of unreacted aluminummetal, dried and During the first thirty minutes of reaction, thehydrogen analyzed. Analysis showed the reaction product to be a mixtureof boehmite and gibbsite in about equal amounts production rate wasidentical with those runs performed without mercuric chloride. However,after the first thirty with a relatively large crystallite size. Thus,high corlccnminutes the reaction rate rapidly decreased and at the endtrations of formic acid fail to yield .a product consisting of one h thti s ub tanti ll inhibit d and essentially of alumina monohydrate andhydrous amorno 1onger l d significant h d phous phases and also gaveboehmite of a large crystallite size, rather than the smaller sizecrystallite material ob- Example 1X tained with lower acidconcentrations. This smaller crystallite size material is oftenadvantageous in catalyst uses This was a repeat of Example VIII with theexception where a greater urfa e area must be presented. that the amountof mercuric chloride added was such that Example VI tggglwas 0.0100 moleHgCl to 0.37 mole of aluminum To a 50 ,P 'P agitated, Steam-jacketedreactor During the first 45 minutes of reaction, the hydrogen fitted wih a refl x condenser was added 3 g ns of production rate was slightlyhigher than that noted in Exionized Water, 2 of 88% formic acid and -pample VIII, but at the end of 1.5 hours the reaction was atomizedalumlllum (995% P Particle $12 fairly completely inhibited and no longerevolved much distribution, BET surface area 310,000 mm. /g.). Therehydrogen.

flCt E under agitation, heated A comparison of the conversion obtainedin Examples mallltamed at At the P of hours an f VIII and IX with thatobtained before the first incremental tional amount of atomized aluminummetal (3.5 lbs. n 3 alumina addition of Example VII is as follows: gal.water) was pumped rnto the reactor. Also at this time the continuousaddition of the 88% formic acid was begun by means of a bellows pump setat a rate to deliver 100 cc./hour. This acid addition was continueduntil a total Conversion (percent) of 1380 cc. of 88% acid had beenadded. E 1 VIII IX VII At 3.5, 4.5, 5 and 6 hours, additions ofalummum-rn- Xampe water slurry were made. Each addition was 1.75 lbs. 125 13.2 1H2 aluminum metal to 1.75 gallons water. The total addition 14,2144 33.38 metal was 14 lbs. in 45 gallons Water. The reaction was 211-15. 7 lowed to continue for 14 hours at the end of which time there wasno unreacted aluminum metal. 5 Analysis of the reaction product showed:3

Example X Amorphous alumma: 27% Boehmite: 73%, crystalllte size 30.0Angstromst The procedure of Example I is followed but using, 0.37 PConcentfaflon, P 2 3 (Theory gram atoms of aluminum, 22.2 gram moles ofwater and 6.58%) 0.53 mole acetic acid, a ratio of 1/7.0/ 420 of theingredi- Example VII ents. Results substantially equal to those of run 1are In this run atomized aluminum metal containing 0.014% obtamed' iron,97.2% of which passed through a 325 mesh screen Example XI was employedalong with 88% formic acid and deionized water. Each reagent wasincrementally added as shown Two runs were performed similar to ExampleI but below. The completion figures are based on the hydrogen withoutthe use of any acid. These runs required the exproduced as measured by awet test meter and may internal application of heat; one being held atC., the clude a small amount of gases produced from the decomother at C.The dionized water had a pH of about position of formic acid. 50 5.3 andafter the aluminum powder was added and stirring Reagents ReactionCompletion Total reaction Aluminum Water Formic acid (88%) time (hours)Before each After each Weight Total Volume Total Volume Total additionaddition (pounds) (percent) (gallons) (percent) (cc.) (percent) 1. 39.2 1. 5 75. 5 250 23. 6 37. 5 0 5 76.2 310 34. s 36.6 270 44.5 61.2 4 565 2. 0 81.0 275 54.1 85.3 245 63.5 82.0 69 5 2. 0 85.7 210 71. 0 89.0240 so. 0 91. 0 6 5 7.0 100 86.2 95.1 380 100.0 93.7 105.2

The product from this run was a milk-white fluid, which begin, the pHrose to that shown below as initial pH.

is thixotropic and has a total concentration of A1 0 of The results wereas follows: 10.84% (Theory 10.98%). X-ray diffraction patterns show thatthis material, after gelation and drying, is 34% I 1 T f 1 P amorphoushydrous alumina and 66% lboehmite having a 70 iiEi reacti ir o.) 11 e rs i oii re iiih r r ird crystallite size of about 18 A. 63 65 M 9&2 23

6.4 75 9.9 95.8 Example VIII The procedure in this experiment wasidentical to that The final pH indicates a considerable solubility ofthe of Example I with the exception that to the initial reac- 75 freshlyprecipitated aluminum hydroxide of 9.9-9.9, which 7 represents a greaterhydroxyl ion concentration than 0.1 N NaHCO which has a pH of about 8.4.The products in each of these runs had only a minor portion of desiredamorphous and boehmite phases.

the above. In the Percent Completion column, the first figure representsthe conversion prior to addition of aluminum; the second figure is thedegree of conversion based upon the total aluminum added.

Total Aluminum added Water Added Formic acid Percent reaction completiontime (hrs.) Wt. Percent total Vol. (gaL) Percent total V01. (cc.)Percent total of reaction Example XII To a three-necked Pyrex flask,fitted with a reflux condenser, an agitator regulated to give 1050r.p.m. a thermoregulator set to maintain temperature of reaction at 100C., was added 400 cc. deionized water (22.2 gin-moles) and grams (0.37gm.-mole) of flaked aluminum metal (99.0% purity, flake size 250420 1.,approximate thickness 0.0001, having a surface area of 600,000 mm. gm.The aluminum metal had a surface coating of stearic acid which was usedas a milling lubricant. To this mixture was added (0.00082 gm.-mo1e)formic acid (as 88% acid). This amounted to 5% of the total formic acidto be added. The thermoregulator was set to 100 C., and the reactionmixture was maintained at this temperature during the course of thereaction. At intervals of 45 minutes, and over a period of 6 hours,additional quantities of 88% formic acid were added, so that the totalformic added was 0.0163 gram-mole. The ratio of materials used in thereaction was 1 mole formic acid to 22.7 gramatoms aluminum to 1360 molesof water; 60 moles of water were used per gram atom of aluminum. Thereaction was continued for a period of 24 hours, at the end of whichtime there was no unreacted aluminum metal remaining. The product wasisolated, by adjusting initial pH (3.6) to 10.4 by means of a 1: 10dilution of concentrated ammonium hydroxide. The resulting slurrycontained 4.52% A1 0 Filtering the precipitated alumina, washing anddrying at 100 C. for 6 hours gave an alumina containing about 0.3% iron,0.02% zinc and 0.05% silicon which showed, by X-ray diffraction, acomposition of 29% amorphous alumina and 71% boehmite of 29 A.crystallite size.

Example XIII evolution measurement and facilities for addition ofreagents, was added a quantity of high purity atomized aluminum metal(99.99% purity, 0.0018% Fe, 5-50 1 particle size distribution, surfacearea of 320,000 mm. g.), approximately 70% of the total water to beutilized and 14% of the total formic acid to be used. The reaction wasinitiated at ambient temperature, raised to 100 C., and maintained atthis temperature during the course of the reaction. During a period of 9hours, aluminum metal was added in a slurry form with water; and theaddition of 88% formic acid continued until the calculated amount offormic acid had been added.

Tabulated below are the experimental data relative to The 104.5%conversion is based on the degree of conversion calculated from awet-test meter. The product was 10.92% A1 0 and showed an X-raydilfraction of: amorphous, 29%; boehmite, 71% ('21 A.).

It can thus be seen that the process of this invention enablesproduction at alumina from aluminum powder under controlled conditionsto give a highly useful alumina product mixture.

It is claimed:

1. A process for the manufacture of an aqueous hydrous alumina slurry,the alumina of which contains both boehmite and amorphous hydrousalumina as determined by X-ray difiraction analysis of the dried solidsof said slurry consisting essentially of reacting finely dividedaluminum having a surface area of about 75,000 to 1 million squaremillimeters per gram with liquid Water in the presence of awater-soluble, lower fatty acid while maintaining the ratio of about 1mole of acid/2-30 gram-atoms of aluminum/ at least about 18 moles ofwater, at a temperature of about 60250 C. and a pressure suflicient tomaintain the liquid phase.

2. The process of claim 1 in which the aluminum powder is in a sizerange of about 5 to 50 microns.

3. The process of claim 1 in which the reaction takes place at atemperature of about -110 C. and about one atmosphere pressure.

4. The process of claim 1 in which the acid is formic acid.

5. The process of claim 4 in which the ratio of reactants is about onemole formic acid/ 5-15 gram-atoms of aluminum/ -750 moles Water.

6. The process of claim 5 in which th aluminum powder is in a size rangeof about 5 to 50 microns and the reaction takes place at a temperatureof about 90-110 C. and about one atmosphere pressure.

7. A process for the manufacture of an aqueous hydrous alumina slurry,the alumina of which contains both boehmite and amorphous hydrousalumina as determined by X-ray diffraction analysis of the dried solidsof said slurry which consists essentially of reacting at a temperatureof about 90 to C. a mixture consisting essentially of water, aluminumhaving a surface area of about 150,000 to 600,000 square millimeters pergram and formic acid sufiicient to impart a pH of about 3 to 4, holdingthe reaction mixture at a temperature of about the boiling point ofwater, incrementally adding aluminum powder and formic acid to maintainsaid pH and temperature and continuing said holding until a mixture ofhydrous alumina and water is obtained having a concentration of about5-12% alumina.

8. The process of claim 7 in which substantially no free aluminumremains when said concentration is reached.

(References on following page) References Cited UNITED STATES PATENTS10/1941 Patrick 23.143

12/ 1943 Connolly 23143 X 5 OSCAR R. VERTIZ, Primary Examiner.

8/ 1956 Bloch 23143 12/1959 Bugosh 23 143 X G. T. OZAKI, Assistant Exammr- 8/1960 Murray et a1. 23-143 12/1965 Hauschild 23-143 OTHER REFERENCES10 Calvert et al.: Societe Chimique de France, Bulletin T. 20, pp. 101and 102 1953).

Newsome at 211.: Alumina Properties," Aluminum Company of America,Pittsburgh, Pa., 1960, pp. 69 and

